When injecting a gas into liquid, it is generally desirable to control the flow of the gas so that the flow is in one direction. Various check valves have been proposed for such purpose.
For example, the use of ozone for water treatment, such as in swimming pools or hot tubs, has become extremely popular. In introducing the ozone into the pool of liquid, it is most common to utilize an ozone generator and a pump to draw air through the generator and produce ozone, which is then pumped directly into the liquid pool or into the return line or recirculating system for the pool of liquid. In such a system, it is desirable to prevent any liquid from flowing back through the gas line and into the ozone generator.
In the past, various types of check valve systems have been proposed for preventing the flow of liquid while accommodating the flow of gases in various types of systems, and the most common type of check valve that is in existence in what is commonly referred to as a spring-biased check valve, in which a valve element is biased to a closed position and is opened by the pressure of the gas or liquid. However, a system as described above cannot utilize a spring-biased check valve since the ozone will rapidly oxidize the parts. Furthermore, since the ozone-generating system operates at extremely low pressures, spring-biased check valves are not suitable for such use. In addition, it has been found that through the passage of time the flow of the ozone through any type of check valve will oxidize the port or valve seat to such an extent as to cause leakage.
Furthermore, most, if not all, commercially-available check valves cannot effectively operate at very low gas flow without leakage. Continuous use of check valves at very low flows will create what is known as a "burning" effect. Thus, as the valve element moves toward the associated valve seat, the relative movement between the element and seat may result in a small path of least resistance between the seat and the element. This small restricted path will result in increases in the velocity of flow, which will have destructive effects on the surface of the valve seat or valve element and will ultimately produce a leak in that area.
In the past, floation plugs have been utilized to effectively seal off the flow of gas upon the application of the back pressure. This floatation plug generally consists of a floating member supported within a housing that is normally in a position spaced from the gas port inlet while gas is flowing through the valve or plug and moves towards the inlet port and seals off the port when liquid is received from the liquid port or into the liquid port. While such types of floating check valves have been proposed, none seem to be fully effective in the above environment. Positive-type of valving is required to protect against backflow.